The industrial robot control safety system must provide a back-up of the fault response link according to the specifications of industrial robot. When the main fault response link fails, the back-up link is enabled. The normal and the back-up fault response links serve as double protection, which is well known as the safety mechanism of industrial robot. The back-up link is also called safety module.
In prior art, duplicating the safety function module is a common approach. The input ports of the two modules receive same signals. The output ports (generally a contactor for controlling strong current) are connected in series to control the power switch, e.g. a contactor. When a safety related warning occurs, the two modules respond to the warning at the same time to, for example, cut off the power supply. Therefore, the two modules back up for each other such that when one of the two modules fails, the other may still respond effectively to achieve safety protection.
The two safety circuits as above-described are substantially the same and work at the same time. Subsequently the circuit aging of the two safety circuits may be synchronous such that the two circuits may both fail at the time, which leads to a safety problem. Besides, the redundant design of two systems may lead to waste of energy and materials.